CustomScrollView Custom Scrolling Flutter - flutter

Question

I have been studing and trying to do some projects and stack in this. So, I created CustomScrollView and the SliverAppBar has to be either fully opened or fully closed. I tried to do but have problems with animation scrolling.
import 'package:flutter/material.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: Scaffold(
appBar: AppBar(
backgroundColor: Colors.deepPurple,
),
body: const MyHomePage(),
),
);
}
}
class MyHomePage extends StatefulWidget {
const MyHomePage({Key? key}) : super(key: key);
#override
State<MyHomePage> createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
final _scrollController = ScrollController();
bool isClosed = false;
#override
void initState() {
super.initState();
_scrollController.addListener(() {
if (_scrollController.offset >= 5 && _scrollController.offset <= 200) {
if (isClosed) {
_scrollController.jumpTo(0);
close();
} else {
_scrollController.jumpTo(202);
close();
}
}
});
}
close() {
setState(() {
isClosed = !isClosed;
});
}
#override
Widget build(BuildContext context) {
return CustomScrollView(
controller: _scrollController,
slivers: [
SliverAppBar(
expandedHeight: 200,
flexibleSpace: SizedBox(
child: Container(
height: 200,
decoration: const BoxDecoration(
image: DecorationImage(
image: NetworkImage(
"https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcS5-OgasVpm-kc2HaOUloxKVlLzLuM6Q53mfA&usqp=CAU"),
fit: BoxFit.cover)),
),
),
),
SliverList(
delegate: SliverChildBuilderDelegate(
(BuildContext context, int index) {
return Container(
color: Color(index),
height: 100,
width: MediaQuery.of(context).size.width,
child: Text("$index"),
);
},
childCount: 10,
))
],
);
}
}
It works when jumpTo is used but has problems when animateTo is used. Thank You!

Answer 1

You need to wrap .animateTo() inside a Future delay.
The below code worked for me
Future.delayed(
Duration(milliseconds: 600),
() {
_scrollController.animateTo(
202,
duration: Duration(
milliseconds: 600),
curve: Curves.ease);
});
Or you can also wrap inside PostFrameCallback
WidgetsBinding.instance.addPostFrameCallback((_) {
_scrollController.animateTo(
202,
duration: Duration(
milliseconds: 600),
curve: Curves.ease);
}